1. Field of the Invention
This invention relates generally to gas separation by electrostatic precipitators and more particularly to baffle assemblies used within the inlet duct and the particle collection hoppers thereof for maintaining the inlet duct free of particles and reducing re-entrainment of particles in the hoppers into the gas stream without interfering with emptying of the hoppers.
2. Description of the Prior Art
As mentioned in the aforementioned co-pending application, the removal of particles from a gas stream by electrostatic precipitators is well known in the art. A typical electrostatic precipitator of the plate type which removes particles from a gas flowing therethrough is illustrated in Ragland Pat. No. 3,425,190. In such precipitators, gas flows through an inlet duct into the precipitator and through gas passages formed between rows of vertical collecting plates. Some precipitators are extremely large and usually include more than one set of laterally spaced collecting plates extending along the length of the precipitator from the inlet to outlet side. A plurality of discharge wire electrodes, electrically insulated from the shell, are suspended within each of the gas passages between the collector electrodes. As the gas passes through the gas passages, the discharge electrodes ionize the particles in the gas which are then attracted to and collected on the vertical collector electrodes. The particles which collect on the collector electrodes are removed therefrom and fall to the bottom of the precipitator. As shown in the Ragland Patent, the bottom of the precipitator contains a plurality of hoppers into which the dust particles fall, are collected, and then removed through the bottom of the hopper.
Preferably, one hopper is suspended under each set of collector electrodes to collect the particles falling from the electrodes in each set. The gas flows beneath the collector electrodes in the associated hopper of each set before being forced back up into the gas passages of the remaining sets of electrodes by the walls of each hopper. In this way, maximum precipitation of the entire gas is assured and particles from the hoppers re-entrained in the gas flowing beneath the collector electrodes are acted upon by the discharge electrodes in the remaining sets.
Although it is preferable to have an individual hopper below each set of collector electrodes, it has been found that it is impractical to do so because of the high cost of manufacturing and installing individual hoppers under each set and because of the cost of the apparatus for hook up to the hoppers to remove the particles. Therefore, one larger hopper is usually placed under two sets of collector electrodes. However, this causes the gas stream flowing beneath the collector electrodes within each hopper to pass by two sets of collector electrodes before it is forced back up into the gas passages by the sides of the hopper. Thus, particle collection is not as efficient as it would be with a hopper under each set of electrodes. To overcome this condition, it is now common practice to secure rigid baffles within each hopper between adjacent sets of collector electrodes which extend downward to a point just above the bottom of the hopper. This baffle system obstructs the flow of gas beneath the collector electrodes and forces the gas back up into the gas passages after it flows beneath only one set of collector electrodes.
However, one disadvantage of this arrangement is that the baffle extending down to the small outlet of the hopper effectively cuts in half the space through which the particles must pass for disposal. The particles falling into the hopper on each side of the baffle assembly tend to lodge between the sides of the hopper and the baffle. In addition, particles which collect and cool in the hopper often tend to form a sticky and thick agglomerate, sometimes even forming a bridge of particles between the wall of the hopper and the baffle. If the particles are allowed to cool too long, they become extremely hard and prevent discharge of the particles from the hopper and must often be manually broken loose by jackhammers or other physical means. The invention of the aforementioned co-pending application overcomes this problem as fully explained therein.
In addition, the inlet ducts that direct the gas into the precipitator usually include gas distrubution baffles to control the distribution of gas flowing into the precipitator. Some of the particles in the gas stream collect on the baffle and eventually fall, or are dislodged by a baffle rapper, onto the bottom of the duct where they collect ahead of the baffle. The particles continue to build up on the duct until they interfere with the flow of gas at which time they must be manually removed such as by shoveling. It should be understood that the precipitator must be shut down during removal of such accumulations.
Accordingly, an object of this invention is to provide improved inlet duct and hopper apparatus for electrostatic precipitators; more particularly, an object is to provide means for preventing the build-up of particles in the inlet duct and to remove such particles during normal operation, to provide a means for preventing particles from lodging between the sides of the hoppers and the hopper baffles, and especially to provide a precipitator having both such means to improve its operation.